The present invention relates to a method for deforming a plastic plate comprising a core of resin-treated fibres, which plate is compressed in a press under elevated pressure and temperature conditions and deformed in a mould.
Such a method is known from European patent application EP 0 705 680 as previously filed in the present applicant's name. According to the method that is known therefrom, a layer package consisting of a core and facing layers laminated on the core on both sides is compressed, using heat, at a pressure of 6 to 90 bar and a maximum temperature of 145 to 160° C. to obtain a plastic plate. During this pressure treatment the resin present in the core layer is not completely cured, so that the plate thus obtained can be deformed in a subsequent heating step. After termination of the pressure treatment the plate is heated asymmetrically in a second step between an upper heating plate, which is heated to a temperature in the range of 150 to 190° C., and a lower heating plate, which has a temperature in the range of 20 to 60° C., with the duration of the heating step being approximately 1 to 10 minutes, dependent on the thickness of the plate. After the plate has thus been asymmetrically heated, it is transferred to a bending unit in which the incompletely cured core layers are plastically deformed, using compression. Finally, to reduce internal stress and to improve the mechanical material properties, the thus deformed plate is transferred to an immersion bath, in which the deformed plate remains fixed in the mould by means of clamps. The post-curing that takes place here at a temperature of 120 to 160° C. is made possible by the fact that the immersion bath consists of a plasticizer. A drawback of such a method of deforming is that three separate operations have to performed, in which especially the post-curing step in the immersion bath is experienced as disadvantageous, especially in view of the chemicals that are used. Moreover, a loss of chemicals occurs upon removal of the deformed plate from the immersion bath, which increases the costs.
From European patent application No. 0 424 909 a method is known in which a plate of cellulose containing particles is obtained through compression and is transformed into a stable final shape by the application of pressure and heat, with the second pressing operation taking place under a significantly higher pressure.
From British patent application No. 2 139 944 a method is known for bending and moulding medium density fibreboard (MDF), in which the MDF plate is first subjected to a softening treatment, using dry or wet heat, and is subsequently bent and fixed in the bent shape by heating to a temperature of 300° C.
From U.S. Pat. No. 4,801,495 granted to the present applicant a decorative panel is furthermore known which comprises a core, with a decorative layer on one or both surfaces of the core, and an outermost layer on at least one surface of the panel, which outermost layer mainly comprises a synthetic resin of one or more radiation-polymerisable compounds. Examples of core materials are non wovens or mats of mineral fibres, paper, fibre glass, synthetic fibres and mixtures thereof.
In addition, from U.S. Pat. No. 4,789,604 granted to the present applicant a decorative panel having at least one matt decorative side is known, which panel comprises a core, with a decorative layer on one or both surfaces of the core, and an outermost layer on at least one surface of the panel, which outermost layer mainly comprises a synthetic resin of one or more radiation-polymerisable compounds. Panels or foils of a plastic material or a metal are mentioned as core materials.